Method of using an optical device for wavelength locking

ABSTRACT

A method of using an optical device. The method comprises splitting a light beam into a first beam that passes through a first arm of a waveguide, and, into a second beam that passes through a second arm of the waveguide. The method also comprises passing at least one of the first beam or second beam through one or more optical resonators that are optically coupled to at least one of the first or second arms. The method also comprises determining a difference in the light-transmittance of the first beam exiting the first arm and the light-transmittance of the second beam exiting the second arm, and, adjusting the operating wavelength if the difference in transmittance exceeds a predefined value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No. 12/611,187filed on Nov. 3, 2009, to Mahmoud Rasras, and entitled, “OPTICAL DEVICEFOR WAVELENGTH LOCKING,” currently allowed; commonly assigned with thepresent invention and incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure is directed, in general, to optical devices andmore specifically, optical wavelength lockers, and, methods of using andmanufacturing the same.

BACKGROUND

This section introduces aspects that may be helpful to facilitating abetter understanding of the inventions. Accordingly, the statements ofthis section are to be read in this light. The statements of thissection are not to be understood as admissions about what is in theprior art or what is not in the prior art.

The efficiency of optical telecommunication systems are enhanced byusing an optical device to monitor and stabilize a wavelength of lightpassing through the system.

SUMMARY OF THE INVENTION

To address some of the above-discussed limitations, one embodiment is amethod of using an optical device. The method comprises splitting alight beam into a first beam that passes through a first arm of awaveguide, and, into a second beam that passes through a second arm ofthe waveguide. The method also comprises passing at least one of thefirst beam or second beam through one or more optical resonators thatare optically coupled to at least one of the first or second arms. Themethod also comprises determining a difference in thelight-transmittance of the first beam exiting the first arm and thelight-transmittance of the second beam exiting the second arm, and,adjusting the operating wavelength if the difference in transmittanceexceeds a predefined value.

Some such embodiments of the method can further include adjusting aresonance frequency of the one or more optical resonators so that anoperating wavelength of the light beam is positioned over a slopedportion of a transmittance curve of the at least one first arm or secondarm optically coupled to the one or more optical resonators. Some suchembodiments can further include adjusting a steepness of thetransmittance curve such that the operating wavelength is centered on asteeper-sloped or a shallower-sloped portion of the transmittance curve.

Some such embodiments of the method can further include passing thefirst beam through a first one of the optical resonators that isoptically coupled to the first waveguide arm. Some such embodiments ofthe method can further include passing the second beam through a secondone of the optical resonators that is optically coupled to the secondwaveguide arm.

Some such embodiments of the method can further include adjusting afirst optical coupler coupled to said first waveguide arm and the firstoptical resonator to change a resonance frequency of the first opticalresonator such that the operating wavelength is centered on a positivelysloped portion of the transmittance curve of said first waveguide arm.Some such embodiments of the method can further include adjusting asecond optical coupler coupled to the second waveguide arm and thesecond optical resonator to change a resonance frequency of the secondoptical resonator such that the operating wavelength is centered on anegatively sloped portion of the transmittance curve of the secondwaveguide arm.

In some such embodiments, at least one of said optical resonators issubstantially athermalized. The substantially athermalized opticalresonator includes a sequence of end-coupled and spaced-apart segmentsof a light-guiding core having a thermo-optic coefficient and opticalmaterial between adjacent ones of the segments. The optical material hasa thermo-optic coefficient of opposite sign than a sign of thethermo-optic coefficient of the spaced-apart segments.

In some such embodiments, combined transmittance curves from a first oneof the optical resonators and a second one of the second opticalresonators includes a v-shaped notch centered in a C or L opticalcommunication band.

In some such embodiments, the adjusting of the operating wavelengthincludes sending a control signal from a control module to a lightsource to cause the light source to emit light at a different saidoperating wavelength.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the disclosure are best understood from the followingdetailed description, when read with the accompanying FIGUREs.Corresponding or like numbers or characters indicate corresponding orlike structures. Various features may not be drawn to scale and may bearbitrarily increased or reduced in size for clarity of discussion.Reference is now made to the following descriptions taken in conjunctionwith the accompanying drawings, in which:

FIG. 1A presents an example optical device of the disclosure having asingle optical resonator;

FIGS. 1B and 1C presents example transmittance curves for waveguide armsof an optical device of the disclosure, such as the device depicted inFIG. 1A;

FIG. 1D presents a detailed view of an example adjustable opticalcoupler of an optical device of the disclosure, such as the devicedepicted in FIG. 1A;

FIGS. 1E-1G present a detailed views of example portion of opticalresonators of an optical device of the disclosure, such as the devicedepicted in FIG. 1A;

FIG. 2A presents an example optical device of the disclosure having twooptical resonators;

FIG. 2B presents example transmittance curves waveguide arms of anoptical device of the disclosure, such as the device depicted in FIG.2A;

FIG. 3 presents a flow diagram of an example method of using an opticaldevice of the disclosure, such as any of the devices discussed in thecontext of FIGS. 1A-2B; and

FIGS. 4A and 4B present example transmittance curves waveguide arms ofan optical device of the disclosure, such as the device depicted in FIG.2A;

FIG. 5 presents a flow diagram of an example method of manufacture anoptical device of the disclosure, such as any of the devices discussedin the context of FIGS. 1A-4B.

DETAILED DESCRIPTION

One embodiment of the present disclosure is an optical device. Someembodiments of the optical device can be configured as, or, to include,a wavelength locker (WL). In some cases, the WL can be used to stabilizeand monitor laser wavelength in telecommunication systems that usewavelength-division multiplexing (WDM). For instance, some embodimentsof the optical device configured as (or to include) a WL, can be used toalign the carrier frequency of the laser to be within about percent ofthe channel spacing of a wavelength-division multiplexed system, such asspecified by the International Telecommunication Union (e.g., theso-called “ITU-Grid”).

Embodiments of the disclosed optical device can be integrated using aplaner lightwave circuit (PLC) platform. This can provide advantages ofeasier mass production and assembly as compared to, e.g., a WL thatincludes etalon-based Fabry-Perot filters or Fiber Bragg Gratings.Integrating the device in a PLC platform also facilitates combinationwith other optical components, such as multiplexers and demultiplexers,photodetectors, and controlling integrated circuits (IC) all on the samesubstrate platform (e.g., an IC chip).

FIG. 1A presents a layout diagram of an example optical device 100 ofthe disclosure. The optical device 100 comprises a 1×2 optical coupler105 on a planar substrate 110, and a waveguide 115 also on the planarsubstrate 110. The waveguide 115 has a first arm 120 and a second arm122 coupled to the 1×2 optical coupler 105. The device 100 also includesan optical resonator 123 also on the planar substrate 110. The opticalresonator 123 is optically coupled to the first arm 120, and, theoptical resonator 123 is substantially athermalized.

The term substantially athermalized as used herein is defined as theresonance frequency of the optical resonator 123 changing by less thanabout 1E-4 nanometers/° C. in the operating wavelength range of thedevice 100 near room temperature (e.g., about 20° C.). For example someembodiments of the device 100 configured as a WL are configured tooperate in one or both the C or L optical communication bands. For thepurposes of the present disclosure, C and L optical communication bandsrefer to a wavelength range of about 1530 nm to 1565 nm, and, about 1565nm to 1625 nm, respectively.

Some embodiments of the 1×2 optical coupler are directional couplers,such as 3 DB directional couplers. Embodiments of the 1×2 opticalcoupler include 50/50 Y-splitters (e.g., coupling coefficient, K=0.5),or couplers such as Mach Zehnder interferometers (MZI). The waveguide115 can be composed of any material used in guiding optical wavelengthsof light, such as semiconductor materials like silicon, dielectricmaterials such as silicates and silica glass used in PLCs, or organicpolymers such as poly(methyl methacrylate (PMMA), fluoropolymers orsilicone polymers.

Some embodiments of the optical resonator 123 include ring resonators,such as all-pass ring resonator filters. The optical resonator 123 canfacilitate monitoring shifts in the wavelength of a light passingthrough the 1×2 coupler 105 to the waveguide 115. Shifts in thewavelength of the light can be detected by comparing the intensity oflight 124 at an output end 127 of the first arm 120 to the intensity oflight 126 at the output end 129 of the second arm 122. E.g., an incominglight can be split equally into the two arms 120, 122 and at least oneof the arms (e.g., first arm 120 in FIG. 1) is optically coupled to theoptical resonator 123.

FIG. 1B shows a portion of an example transmittance curve, as a functionof wavelength, for the arm 120 coupled to the optical resonator 123(FIG. 1A). The operating wavelength can be located on a positivelysloping part of the curve, although in other example embodiment theoperating wavelength of the light-source can be located on a negativelysloping part.

For the embodiment shown in FIG. 1A, the light passing through the otherarm is not filtered, e.g., the second arm 122 is not coupled to anoptical resonator. FIG. 1C shows a portion of an example transmittancecurve for the arm 122 not coupled to the optical resonator 123. As shownin FIG. 1C, the transmittance curve is substantially constant as afunction of wavelength.

As further illustrated in FIG. 1A, some embodiments of the device 100can further include first and second photo-detectors 130, 132 located onthe planar substrate 110. The first and second photo-detectors 130, 132are optically coupled to output ends 127, 129 of the first and secondarm 120, 122 of the waveguide 115, respectively. In some embodiments,the first and second photo-detectors 130, 132 are germanium-containingphotodiode detectors, but other detector type, familiar to those skilledin the art could be used. The photo-detectors 130, 132 also canfacilitate monitoring shifts in the wavelength of a light. For instance,the light intensity at the ends 127, 129 of each of the arms 120, 122monitored by one of the photo-detectors 130, 132. For the exampleembodiment depicted in FIGS. 1A-1C, if the light's wavelength is shiftedto a longer wavelength, the voltage (V) generated at the firstphoto-detector 130 will increase, while the voltage (V) at the secondphoto-detector 132 will remain constant.

As further illustrated in FIG. 1, some embodiments of the device 100 canfurther include a control module 135 located on the planar substrate110. The control module 135 can be electrically coupled to the first andsecond photo-detectors 130, 132. The control module 135 can be orinclude electronic circuitry located on the planar substrate 110 (e.g.,an integrated circuit comprising an amplifier component 137 (e.g., adifferential amplifier) and a control component 138) configured todetect the difference in currents from the photo-detectors 130, 132. Thecontrol module 135 can be configured to control an output wavelength ofa light-source 140, e.g., optically coupled to the 1×2 optical coupler105. Continuing with the example embodiment depicted in FIGS. 1A-1C, ifthe light shifts to a longer wavelength then the increased voltage, orother electrical signal, from the first photo-detector 130 to thecontrol module 135 can increase compared to the voltage from the secondphoto-detector 132. If the different exceeds a defined threshold, thecontrol module 135 can be configured to send a control signal 142 to thelight-source 140 thereby causing a decrease the wavelength of lightemitted by the light-source 140.

As further illustrated in FIG. 1A, in some embodiments of the device100, the optical resonator 123 further includes an adjustable opticalcoupler 145 optically coupled to the first arm 120 and to alight-guiding core of the resonator 123 (e.g., the light-guiding core ofa ring resonator). For instance as shown in the inset drawing FIG. 1D,in some embodiments, the adjustable optical coupler 145 can beconfigured as a MZI, such as a balanced MZI having a thermo-optic phaseshifter 146 coupled to one of the two arms 147, 148 of the MZI. Theadjustable optical coupler 145 can be used to adjust the opticalcoupling strength of the resonator 123 to the arm 120 and therebyfacilitate adjusting the device's 100 sensitivity towards detecting achange in the wavelength of the light. For instance, a decrease inoptical coupling can increase the slope of the transmittance curve (FIG.1B), while an increase in optical coupling can decrease the slope.

As also show FIG. 1A, some embodiments of the optical resonator 123further includes a phase shifter 150. In some embodiments the phaseshifter 150 is configured as a thermo-optic phase shifter, e.g., as ametal contact coupled to the light-guide core of a ring resonator 123.The phase shifter facilitates tuning of the optical resonator 123 andthereby facilitates adjusting the device's 100 sensitivity towardsdetecting a change in the wavelength of the light. For instance, theoptical resonator's 123 resonance frequency can be adjusted such thatthe wavelength of the light is located on a positively or negativelysloped portion of the transmittance curve such as depicted in FIG. 1B.

As illustrated in the inset diagrams shown in FIGS. 1E and 1F, in someembodiments the substantially athermalized optical resonator 123includes a light-guiding core which includes a first core portion 160with a positive thermo-optic coefficient, and, a different portion whichincludes a second core 162 with a negative thermo-optic coefficient. Forinstance, in some embodiments the first core portion 160 materialincludes silicon and the second core portion 162 material includes apolymer. Examples of suitable materials that can have negativethermo-optic coefficient include fluoroacrylate polymers or siliconepolymers. The first and second core portions 160, 162 can becompositions of different materials (e.g., different types offluoroacrylate or silicone polymers) to adjust the refractive index andthermo-optic coefficient to the appropriate value, e.g., to match theindexes of the first and second cores 160, 162.

An athermalized optical resonator 123 configured to have a light-guidingcore with one or more of the first and second core portions 160, 162with positive and negative thermo-optic coefficients, respectively,helps avoid the need to used thermo-electric temperature controllers toprovide a thermally stable device 100. For instance, to minimize theeffects of surrounding temperature variations on the device 100, thesecond core portion 162 of polymer material can be used to replacesections of a first portion core material 160 made of silica in a ringresonator 123. An appropriate length of polymer core second portions 162of negative thermo-optic index coefficient can compensate for the silicawaveguide portions 160 of positive thermo-optic index coefficient. Insome embodiments where the device 100 further includes a phase shifter150 optically coupled to the resonator 123, it can be advantageous forthe phase shifter 150 to be optically coupled to a portion of thelight-guiding core 160 of the resonator 123 that does not include thesecond core 162. For instance when the phase shifter 150 is configuredas a thermo-optic phase shifter can be desirable for the second core 162comprising polymer materials such as silicone, to be thermally isolatedfrom any local heating effects from the phase shifter 150.

Examples of such configurations for the resonator core 160, 162 areshown in FIGS. 1E and 1F. For a length of resonator core composedprimarily of the material with the positive thermo-optic coefficient(e.g., a known length silica or silicon core 160), it is possible tocalculate how the wavelength response of the first core portion 160material will change per degree change in temperature. One can then addto, or replace some of, the material of the first core portion 160 withthe material of the second core portion 162 (e.g., polymer material).The amount added or replaced is such that, e.g., if the ambienttemperature changes by one degree, the second portion 162 will add anegative phase shift to adjust for this difference in temperature tocompensate for the positive phase shift from the first portion 160.

By way of example, the length of the polymer portion 162 of theresonator core can be calculated such that

${{\frac{}{t}\left( {{n_{p}\Delta \; L_{p}} + {n_{s}L_{r}}}\; \right)} = 0},$

from which:

${{\Delta \; L_{pol}} = {{- L_{r}}\frac{\left( {\frac{n_{s}}{T} + {n_{s}\alpha}} \right)}{\left( {\frac{n_{p}}{T} + {n_{p}\alpha}} \right)}\mspace{14mu} \ldots}}\mspace{14mu},$

where n_(s) and n_(p) are the silica and the polymer indices,respectively. ΔL_(p) is the length (or sum of lengths of differentsegments) of polymer waveguide portions of core 162, L, is the ringresonator's 123 circumference, and α is the substrate's 110thermo-expansion coefficient. For example, if the ring resonators 123having a first portion core 160 of silica has a circumference of 3 mm,n_(s)=1.464, n_(p)=1.4459,

${\frac{n_{s}}{T} = {1.8^{- 5}}},{{{and}\mspace{14mu} \frac{{np}}{T}} = {{- 3.6}^{- 4}}},$

then ΔL_(P) should be about 150 μm to substantially athermalize theresonator 123.

Poor mode-matching between the first core portions 160 and second coreportions 162 can cause propagation losses due to light diffraction. Asillustrated in FIG. 1E, to reduce propagation losses when coupling lightfrom the first core portions 160 to the second core portions 162,separate segments of the second core portions 162 can be interleavedwith separate segments of the first core portions. In some cases,propagation losses can be further minimized by having separate segmentsof the second core portions 162 progressively decrease in length movingin a direction away from a central region 165 of the second coreportions 162.

Additionally or alternatively, as illustrated in FIGS. 1E and 1F, toreduce propagation losses when coupling light from the first coreportions 160 to the second core portions 162, the first core portions160 can be progressively decreased in widths 169 in a direction movingaway from interfaces 167 between the first core and the second coreportions 160, 162. Tapering the widths 169 of the first core portion 160in this fashion helps to mode match the first and second core portions160, 162.

In some embodiments, such as shown in FIG. 1G. the substantiallyathermalized optical resonator 123 includes a portion 170 of alight-guiding core 160 clad by a first cladding material 172 having apositive thermo-optic coefficient, and, a different portion 174 of thelight-guiding core 160 clad by a second cladding material 176 having anegative thermo-optic coefficient. In FIG. 1G, portions of the first andsecond claddings were not depicted so that the underlying core 160 couldbe depicted. The core 160 of the resonator 123 can be composed of a samelight-guiding core material (e.g., silicon or silica). Alternatively,the core can be composed of core portions composed of differentmaterials, e.g., core portions 160, 162 such as discussed in the contextof FIGS. 1E and 1F, although propagation losses may not favor suchconfigurations.

One skilled in the art would be familiar with computerized simulatedbeam propagation methods that could be used to determine desired lengthsof segments or the extents of tapering of the first and second coreportions 160, 162, or, of the lengths and optical index coefficients ofthe first and second claddings 172, 176 to optimize mode matching forthe various configurations depicted in FIGS. 1E-1G.

FIG. 2A presents a layout diagram of another example optical device 200of the disclosure. The optical device 200 comprises the 1×2 opticalcoupler 105, waveguide 115, the optical resonator 123 coupled to thefirst arm 120 of the waveguide 115, photodetectors 130, 132, and controlmodule 135 on the planar substrate 110, such as discussed in the contextof FIG. 1A. Additionally, the device 200 comprises a second opticalresonator 205 on the planar substrate 110, the second optical resonatorbeing optically coupled to the second arm 122 of the waveguide 120. Insome embodiments, one or both of the optical resonators 123, 205 aresubstantially athermalized, e.g., using configurations discussed in thecontext of FIGS. 1E-1G. In some embodiments, the second opticalresonator 205 also comprises an adjustable coupler 145 and phase shifter150.

A device 200 having first and second optical resonators 123, 205 canprovide the advantages of greater sensitivity and tune-ability over adevice 100 with a single resonator 123. FIG. 2B, shows portions ofexample transmittance curves as a function of wavelength, for the firstand second arm 120 122 coupled to the optical resonators 123, 205,respectively. The wavelength of the light can be located on a positivelysloping part of the transmittance curve for the first arm 120 andoptical resonator 123, and also located on a negatively sloping part ofthe transmittance curve for the second arm 122 and optical resonator205. For instance, the combined transmittance curves from the opticalresonator 123 and the second optical resonator 205 can includes av-shaped notch 210 that is centered, e.g., in the C or L opticalcommunication bands. Consequently the sensitivity of such devices 200 todetect wavelength shifts can be greater than, e.g., a device 100 with asingle optical resonator 123. In turn, the control module 135 canthereby more precisely control the output wavelength of the light-source140 optically coupled to the 1×2 optical coupler 105, e.g., via thecontrol signal 142.

Moreover, in embodiments where both of the optical resonators 123, 205can be tunable optical resonators (e.g., each with their own opticalcoupler adjustable optical coupler 145 and phase shifter 150). Thedevice's 200 sensitivity can be adjusted over a broader range ascompared to e.g., a device 100 with a single tunable optical resonator123. The device 200 can also be configured to operate over a widerwavelength range, e.g., by designing the full spectral range of theresonators 123, 205 to match the channel spacing of a WDM system.

Embodiments of the optical device can include other components tofurther monitor and control the optical output from the light-source140. For instance, as shown in FIGS. 1A and 2A, the devices 100, 200 caninclude an input waveguide 180 on the planar substrate 110. One end 182of the input waveguide 180 can be optically coupled to the light-source140 and another end 184 of the input waveguide 180 can be opticallycoupled to the 1×2 optical coupler 105. A tap port 185 can be opticallycoupled to the input waveguide 180 (e.g., at or before the end 184). Thetap port 185 can be configured to route a portion of a light (e.g.,about 5 percent in some cases) from the light-source 140 to the controlmodule 135 (or to a separate control module, not shown) which isconfigured to adjust light-transmission intensity from the light-source145. For instance, the light routed to tap port 185 can be transferredto another photo-detector (not shown) which, in turn, is configured tosend a signal which is proportional to the intensity of the light to thecontrol module 135.

Another embodiment of the disclosure is a method of using an opticaldevice. FIG. 3 presents a flow diagram of an example method of using anoptical device, such as any of the devices 100, 200 discussed in thecontext of FIGS. 1A-2B. With continuing reference to FIGS. 1A-2A, themethod comprises a step 310 of splitting a light beam (e.g., via a 1-2coupler 105, FIG. 1A or 2A) having some desired operating wavelengthinto a first beam that passes through a first arm 120 of a waveguide 115and into a second beam that passes through a second arm 122 of thewaveguide 115.

The method also comprises a step 310 passing at least one of the firstor second light beams through one or more optical resonators 123 (andoptionally, resonator 205) that are optically coupled to at least one ofthe first or second arms 120, 122. For instance, in some cases passingthe light beam in step 310 includes passing the first beam through afirst one of the optical resonators (e.g., resonator 123, FIG. 1A) thatis optically coupled to the first arm 120, and, passing the second beamthrough a second one of the optical resonators (e.g., resonator 205,FIG. 2A) that is optically coupled to the second arm 205.

The method also comprises a step 315 of adjusting a resonance frequencyof the one or more optical resonators 123 (e.g., including optionalresonator 205) so that the operating wavelength is positioned over asloped portion of a transmittance curve (see e.g., FIGS. 1B-C and 2B) ofthe one or more optical resonators 123, 205. In some cases, adjusting aresonance frequency in step 315 includes adjusting the phase of theresonator 123 (including optionally, resonator 205), e.g., via a phaseshifter 150 coupled to the core of the resonator 123.

The method also comprises a step 320 of determining a difference inlight-transmittance of the first beam (e.g., beam 124, FIG. 1A, 2A)exiting the first arm 120 (e.g., at end 127) and light-transmittance ofthe second beam (e.g., beam 126, FIG. 1A, 2A) exiting the second arm 122(e.g., at end 129). For instance, as part of step 320 thelight-transmittance of the light beams can be converted into voltages(V, FIGS. 1A, 2A) using photo-detectors 130, 132, and the voltages canbe compared using a differential amplifier component 137 of a controlmodule 135.

The method also comprises a step 325 of adjusting the operatingwavelength if the difference in light-transmittance intensities exceedsa predefined value (e.g., greater than one percent in some cases). Forinstance, as part of step 325 if there is a voltage differencedetermined by the differential amplifier component 137 that exceeded apre-defined value (e.g., an about 1 percent difference), then a controlcomponent 138 of the control module can send a control signal 142 to alight-source 140 which in turn causes the light-source 140 to emit lightat a higher or lower wavelength.

Some embodiments of the method of use further include a step 330 ofadjusting a steepness of a transmittance curve of the one or moreoptical resonator 123 (and optionally, resonator 205) such that theoperating wavelength of the light-source 140 is centered on asteeper-sloped or a shallower-sloped portion of the transmittance curve.For instance, FIGS. 4A and 4B present portions of example transmittancecurves of two optical resonators (e.g., resonators 123, 205 in FIG. 2A).Adjusting the extent of optical coupling of the resonator 123 and secondresonator 205 with optically coupled arm 120 and second arm 122,respectively, can produce either the transmittance curves in FIG. 4A orin FIG. 4B. For instance, reducing the optical coupling (e.g., via anadjustable couplers 145) can transform the transmittance curves fromthat shown in FIG. 4A to that shown in FIG. 4B.

FIGS. 4A and 4B also illustrate embodiments of adjusting the resonancefrequencies of optical resonators 123, 205, as part of step 315. Suchembodiments can further include a step 340 of adjusting a first opticalcoupler 145 coupled to the first arm 120 and the first optical resonator123 to change a resonance frequency of the first optical resonator 123such that the operating wavelength is centered on a positively-slopedportion of the transmittance curve of the first optical resonator 123.Such embodiments can also include a step 342 of adjusting a secondoptical coupler 145 coupled to the second arm 120 and the second opticalresonator 205 to change a resonance frequency of the second opticalresonator 205 such that the operating wavelength is centered on anegatively-sloped portion of the transmittance curve of the secondoptical resonator 205.

Another embodiment of the disclosure is a method of manufacturing anoptical device. FIG. 5 presents a flow diagram of an example method ofmanufacturing an optical device, such as any of the devices 100, 200discussed in the context of FIGS. 1A-4B.

The method comprises a step 505 of providing a planar substrate (e.g.,substrate 110, FIG. 1A, 2A), wherein the planar substrate includes alight-guiding layer located on a light-cladding layer. For example,providing the substrate can include providing a silicon-on-insulatorsubstrate, or blanket depositing a cladding layer of silicon oxide onthe planar substrate and blanket depositing a light-guiding layer ofsilicon on the silicon oxide cladding layer.

The method also comprises a step 510 of patterning the light-guidinglayer to form light-guiding cores of one or more optical resonators(e.g., resonators 123, 205, in FIGS. 1A and 2A). In some cases, thepatterning the light guiding layer in step 510 further includespatterning the light-guiding layer to form light-guiding cores of a 1×2optical coupler (e.g., coupler 105, in FIGS. 1A and 2A), of a waveguidehaving first and second arms (e.g., waveguide 115, having arms 120, 122,in FIGS. 1A and 2A). The cores of first and second arms are both coupledto the 1×2 optical coupler core, and the cores of the one or moreoptical resonators 123, 205 that are separately optically coupled to thefirst arm 120 or second arm 122, respectively. In some cases, thepatterning step 510 further includes patterning adjustable opticalcouplers that are optically coupled to the resonators (e.g., adjustableoptical couplers 145 in FIG. 1A, 1D, 2A).

The method further comprises a step 515 of substantially athermalizingat least one of the optical resonator cores.

In some cases, substantially athermalizing in step 515 further includesa step 520 of removing a portion of the at least one optical resonatorcores (e.g., portions of the resonator core 160, 162, FIG. 1E, 1F), and,a step 525 of depositing a second light-guiding layer on the regionpreviously occupied by the removed portion. The second light-guidinglayer has a thermo-optic coefficient with an opposite sign to athermo-optic coefficient of the first light-guiding layer. For instancein some cases, the first light-guiding layer can include a silicon orsilicon oxide layer having a positive thermo-optic coefficient, whilethe second light-guiding layer can include a silicone layer having anegative thermo-optic coefficient. In other cases, the firstlight-guiding layer can include a silicone layer having a negativethermo-optic coefficient, while the second light-guiding layer caninclude a silicon or silicon oxide layer having a positive thermo-opticcoefficient. Substantially athermalizing in step 515 can further includea step 530 of patterning the second light-cladding layer to formreplacement portions of the at least one optical resonator cores (e.g.,the second core portions 162 of FIG. 1E or 1F).

In some cases, substantially athermalizing in step 515 further includesa step 535 of covering at least one of the light-guiding opticalresonators cores of one or more optical resonators cores with a claddinglayer. The cladding layer has a thermo-optic coefficient with anopposite sign to a thermo-optic coefficient of the at least onelight-guiding optical resonator cores. For instance, in some cases thelight-guiding optical resonators core can be composed of silicon orsilicon oxide having a positive thermo-optic coefficient, while thecladding can be composed of silicone having a negative thermo-opticcoefficient. In other cases, the light-guiding optical resonators corecan be composed of silicone having a negative thermo-optic coefficient,while the cladding can be composed of silicon or silicon oxide having apositive thermo-optic coefficient.

One skilled in the art would be familiar with other steps that could beperformed to form other components of the optical device, includingforming phase shifters that are coupled to the resonators or to theadjustable optical couplers of the device, from the photo-detectors onthe substrate, or forming the control module of the substrate, andprovided a light-source, such as a laser light-source.

Although the embodiments have been described in detail, those ofordinary skill in the art should understand that they could make variouschanges, substitutions and alterations herein without departing from thescope of the disclosure.

What is claimed is:
 1. A method of using an optical device, comprising:splitting a light beam into a first beam that passes through a firstwaveguide arm of a waveguide structure and into a second beam thatpasses through a second waveguide arm of said waveguide structure;passing at least one of said first beam or second beam through one ormore optical resonators that are optically coupled to at least one ofsaid first waveguide arm or said second waveguide arm; determining adifference in light-transmittance of said first beam exiting said firstwaveguide arm and light-transmittance of said second beam exiting saidsecond waveguide arm; and adjusting said operating wavelength if saiddifference exceeds a predefined value.
 2. The method of claim 1, furtherincluding adjusting a resonance frequency of said one or more opticalresonators so that an operating wavelength of said light beam ispositioned over a sloped portion of a transmittance curve of said atleast one first waveguide arm or second waveguide arm optically coupledto said one or more optical resonators.
 3. The method of claim 2,further including adjusting a steepness of said transmittance curve suchthat said operating wavelength is centered on a steeper-sloped or ashallower-sloped portion of said transmittance curve.
 4. The method ofclaim 1, further including: passing said first beam through a first oneof said optical resonators that is optically coupled to said firstwaveguide arm; and passing said second beam through a second one of saidoptical resonators that is optically coupled to said second waveguidearm.
 5. The method of claim 1, further including: adjusting a firstoptical coupler coupled to said first waveguide arm and said firstoptical resonator to change a resonance frequency of said first opticalresonator such that said operating wavelength is centered on apositively sloped portion of said transmittance curve of said firstwaveguide arm; and adjusting a second optical coupler coupled to saidsecond waveguide arm and said second optical resonator to change aresonance frequency of said second optical resonator such that saidoperating wavelength is centered on a negatively sloped portion of saidtransmittance curve of said second waveguide arm.
 6. The method of claim1, wherein at least one of said optical resonators is substantiallyathermalized, said substantially athermalized optical resonatorincluding: a sequence of end-coupled and spaced-apart segments of alight-guiding core having a thermo-optic coefficient, and, opticalmaterial between adjacent ones of said segments, said optical materialhaving thermo-optic coefficient of opposite sign than a sign of saidthermo-optic coefficient of said spaced-apart segments.
 7. The method ofclaim 1, wherein combined transmittance curves from a first one of saidoptical resonators and a second one of said second optical resonatorsincludes a v-shaped notch centered in a C or L optical communicationband.
 8. The method of claim 1, wherein said adjusting of said operatingwavelength includes sending a control signal from a control module to alight source to cause said light source to emit light at a differentsaid operating wavelength.